Joint Throughput and Fault Tolerance Requirement for Cost-Effective Dense WiFi

A dense WiFi uses numerous access points (APs) to provide Internet access to many users in an indoor site (such as concert hall or stadium). To deploy dense WiFi, the existing approach adopts two separate QoS requirements: (i) ensuring a minimum throughput for each station, and (ii) ensuring fault tolerance by withstanding the failure of at most N APs where N is a given value. We observe that these separate requirements lead to costly dense WiFi because the number of required APs increases by about N times. To address this issue, we propose a joint throughput and fault tolerance requirement (or joint requirement) to construct cost-effective dense WiFi. This joint requirement ensures that the throughput of each station is at least rho(i) when any i APs fail, where rho(i) is a given value and i = 0, 1, 2, .... For example, when no AP fails, the per-station throughput is at least rho(0) = 5 Mbps; when any one AP fails, the per-station throughput is at least rho(1) = 3 Mbps; when any two APs fail, the per-station throughput is at least rho(2) = 1 Mbps. To realize this joint requirement, we formulate and solve an optimization problem for AP placement and resource allocation. The objective is to minimize the number of APs required while fulfilling the joint requirement. Simulation results demonstrate that the joint requirement offers desirable tradeoff between cost and performance, making dense WiFi more cost-effective.